Interpretive Summary: Dietary oils are composed of different types of fatty acids. These fatty acids are saturated, monounsaturated and polyunsaturated. Some fatty acids are essential. One fatty acid that is essential is alpha-linolenic acid which is part of a group of fatty acids known as omega-3 fatty acids. They are called omega-3 because of the location of the first unsaturated bond in the fatty acid molecule. Alpha-linolenic is the precursor of two long chain polyunsaturated omega-3 fatty acids known as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). It has been suggested that the omega-3 fatty acids, especially EPA and DHA, are beneficial for bone formation and maintenance, but the benefits of omega-3 fatty acids have not been consistent. Boron, a mineral found in fruits, vegetables, nuts and pulses, also has been shown to be beneficial to bone formation and maintenance, but the magnitude of the effect is often modified by other dietary factors. Because boron, EPA and DHA is thought to have similar actions in the body, an experiment was performed to determine whether changes in bone composition, shape and strength induced by boron deprivation are influenced by the fatty acid content of the diet, or that some beneficial effects of omega-3 fatty acids on bone are prevented by boron deprivation. Female rats were fed through gestation and lactation and pups were fed 13 weeks post weaning diets low (deficient) or supplemented (adequate) in boron and with dietary oil either palm (very low in omega-3 fatty acids) or canola oil (high in the omega-3 fatty acid, alpha-linolenic acid). Dietary oil affected femur shape and strength of the pups through an interaction with boron. Long bone (femur) breaking resistence (strength) and flexibility were lowest in boron-deprived females fed canola oil but were greatest in boron-supplemented females fed canola oil. Dietary boron did not affect breaking resistance of bones from rats fed palm oil. Both boron and dietary oil affected the concentration of minerals in bone that are usually associated with the organic matrix, the area in which bone is formed. The findings suggest that a diet high in the omega-3 fatty acid, alpha-linolenic acid, promotes bone strength best when the diet contains foods high in boron, and that some of positive interaction may be the result of changes in bone organic matrix composition.

Technical Abstract:
Female and male rats weighing about 170 g and 200 g, respectively, were fed diets (~70 ug boron/kg) in a factorial arrangement with supplemental boron at 0 (deficient) and 3 (adequate) mg/kg and canola oil or palm oil at 75 g/kg of diet as variables. After 5 weeks, six females in each treatment were bred. Dams and pups continued on their respective dietary treatments through gestation, lactation and post-weaning. Thirteen weeks after weaning, plasma and bones were collected from 12 male and 12 female offspring in each treatment. Boron supplementation increased femur strength measured by the breaking variable bending moment; tibial calcium and phosphorus concentrations; and plasma alkaline phosphatase. Femur breaking stress was greatest in boron-supplemented rats fed canola oil, and lowest in boron-deprived females fed canola oil; this group also exhibited the lowest femur bending moment. Minerals associated with bone organic matrix, zinc and potassium, were increased by boron supplementation in tibia. Plasma phospholipids were decreased by boron deprivation in females, but not males. Plasma cholesterol was decreased in boron-supplemented males by replacing canola oil with palm oil. The findings suggest that a diet high in omega-3 alpha-linolenic acid promotes femur strength best when the dietary boron is adequate.